Method for leaching copper concentrate

ABSTRACT

This invention relates to a method where sulfidic iron-bearing copper concentrate is leached on the countercurrent principle, in a chloride environment. The leaching takes place with the aid of bivalent copper and an oxygen-bearing gas as a multistage continuous process, under normal pressure, at a temperature, which as highest corresponds to the boiling point of the solution. Part of the insoluble solid matter is returned, counter to the main flow of solid matter, to one of the previous leaching stages or reactors where, as a result of the extended leaching time, the leach waste iron is recovered mostly as hematite.

[0001] This invention relates to a method where sulfidic iron-bearingcopper concentrate is leached on the countercurrent principle, in achloride environment. The leaching takes place with the aid of bivalentcopper and an oxygen-bearing gas as a multistage continuous process,under normal pressure, at a temperature which at highest corresponds tothe boiling point of the solution. Part of the insoluble solid matter isreturned, counter to the main flow of solid matter, to one of theprevious leaching stages or reactors where, as a result of the extendedleaching time, the leach waste iron is recovered mostly as hematite.

[0002] Countercurrent leaching of a copper-bearing raw material, such assulfidic concentrate, is described in the prior art, for example in U.S.Pat. No. 5,487,819. The sum reaction of the copper pyrite/chalcopyriteleaching is given in the publication as follows:

CuFeS₂+Cu²⁺+¾O₂+½H₂O=FeOOH+2Cu¹⁺++2S⁰  (1)

[0003] From the reaction it can be seen that the iron is removed fromthe leach as goethite precipitate. Later on, in an article concerningthe same process; P. K. Everett: “Development of the Intec CopperProcess by an International Consortium, Hydrometallurgy 1994, IMM-SCI,Cambridge, England, 11-15 July 1994”, it is noticed, that leaching takesplace in three stages at a temperature of about 80-85° C. and thegoethite obtained is akaganeite, or beta-goethite (β-goethite).Furthermore, in the article describing the same process; A. J. Moyes etal: “Operation of the Intec Copper ‘One’ TPD Demonstration Plant, Alta1998 Copper Sulphides Symposium, Brisbane, Australia, Oct. 19, 1998”,there is a flowchart of the process on page 19. According to thisflowchart the countercurrent leaching takes place in three stages, ineach of which there are three reactors, and precipitation is carried outbetween the stages.

[0004] According to the basic literature of chemistry, akaganeite isgoethite in its metastable form, which on this basis, is not anespecially beneficial form for waste. It is known in the hydrometallurgyof zinc, that iron precipitate can take three forms: jarosite, goethiteor hematite. It is also known that hematite is the most stable compoundand is thus the correct means of disposal in the long run. Thedisadvantage of hematite has been, however, the fact that it is the mostexpensive to manufacture, since hematite requires autoclave conditionsfor its formation. On page 223 of the article by F. W. Schweitzer et al:“Duval's CLEAR Hydrometallurgical Process, Chloride Electrometallurgy,AIME, 1982, New York”, it is mentioned that hematite is formed at atemperature above 150° C.

[0005] We have also noticed that, in countercurrent leaching accordingto the prior art described above, the capacity of the leaching reactorsis not utilized to the full. In the method the solid matter travelsstraight through the leaching equipment, but in relation to the leachingof solid matter, this propagation rate is not the optimum. From thestandpoint of the leaching of solid matter, it is preferable to have aslong a delay as possible.

[0006] The developed method relates to the leaching of a sulfidic,iron-bearing copper concentrate in a chloride milieu, to achieve anessentially iron-free, alkali chloride-copper chloride solution and torecover the iron as precipitate. The leaching is carried outcontinuously on the countercurrent principle and in several stages. Thecopper concentrate is leached in atmospheric conditions at atemperature, which at highest corresponds to the boiling point of thesolution, and the iron in the concentrate is precipitated mainly ashematite. The essential features of the invention are presented in theenclosed patent claims.

[0007] It is characteristic of the present invention, that theconcentrate is leached by long delay. By long delay is meant, that theleaching time of the solid matter is clearly longer than theflow-through time of the process solution in the opposite direction. Along solid-matter leaching time is possible to achieve by recycling, orreturning, the solid matter from the leaching stage, against thedirection of propagation of the main flow of the other solid matter, orby recycling, or returning, the solid matter within any leaching stage.Returning the solid matter to leaching enables the formation ofhematite, since we have noticed that iron can precipitate as hematite inatmospheric conditions, if the leaching time of the solid matter issufficiently long and the solid matter content is sufficiently high. Thelong leaching time resulting from solid matter recycling also allows thefullest possible utilization of the capacity of the leaching reactors.

[0008] So, according to the developed method, the solid matter isrecycled in the process by returning it from the end of the process tothe beginning. Thus, within any stage of the process comprising severalreactors, the solid matter is returned from reactors of the final end ofthe stage to a reactor at the beginning, or recycling can be realizedeven in a single reactor. At the end of every stage, or after thereactor, the separation of liquid and solid matter takes place,generally by means of a thickener. The solution, the overflow, producedbetween the stages from separation, is conducted to the previous stagein regard to the flow direction of the solid matter and the solid matterprecipitate, the underflow, mostly to the next leaching stage. Accordingto the invention now, part of the underflow of one or every stage isreturned to any previous or to the same leaching stage to any reactor,preferably to the first reactor.

[0009] According to our experience, when using commercial concentrates(25% Cu), it is preferable that the solid matter content in the firstreactor of the stage is at least 250 g/l. Recycling of the solid mattercreates favorable conditions for the nucleation and crystal growth ofhematite. According to the invention, the solid matter is recycled insuch a way that the leaching time of the solid matter is at least twice,preferably three times that of the leaching where the solid matter isnot recycled, or returned. In our experience the formation of hematiterequires at least 10 hours' leaching time.

[0010] When copper concentrate is leached in a chloride milieu, the ironcontained in the concentrate dissolves first as bivalent, butoxygen-bearing gas, such as air, is blown into the leaching reactors, sothat the leached iron oxidizes into trivalent and precipitates from thesolution. In addition, the precipitate contains sulfur of the rawmaterial as elemental. As stated above, iron can be precipitated ashematite even in atmospheric conditions, when the leaching time issufficiently long and enough precipitation nuclei are present. Hematiteand goethite differ clearly in color, —goethite is gray and hematitered—so they are clearly identifiable on the basis of color.

[0011] The method of the present invention is further described withreference to the enclosed example.

EXAMPLE

[0012] A comparison was made between the method of the present inventionand traditional technology, and two test campaigns were carried out. Inboth test campaigns the method was tested in a three-stage process. Inthe first and in the last stages there was one reactor and in the secondthere were two reactors, in other words, four reactors altogether.Between all stages there was a thickener, from which the solid matterwas led to the following stage and the solution obtained as thickeneroverflow was conducted to the previous stage. The reactors and stagesare numbered according to the flow direction of the solid matter. In thetest campaign, a NaCl-CuCl solution was fed into the last reactor, R4,and the chalcopyrite concentrate into the first reactor, R1. The resultsare presented in Table 1.

[0013] Test campaign 1 was countercurrent leaching according to theprior art, which was carried out in reactors, all of which were of 10liters. Solid matter was neither recycled between nor within the stages.The temperature of the reactors was maintained at 95° C.

[0014] Test campaign 2 is an example of an adaptation of the methodaccording to the invention in countercurrent leaching. There were alsofour reactors in test campaign 2, and the capacity of all reactors was 5liters. The temperature of the reactors in test campaign 2 wasmaintained at 85° C. In this test campaign the solid matter was recycledwithin the same stage so that the thickener underflow of each stage wasrecycled to the first reactor of the same stage. As can be seen in Table1, the solid matter content was two-three times that of test campaign 1.Thus a delay built up for the solid matter, which was almost three timeslonger compared to the delay in test campaign 1.

[0015] From the test campaigns it can be seen that an equally goodrecovery was more or less gained in all runs, but the first campaignrequired reactors, which were 100% larger and a temperature 10° C.higher. It can also be concluded from test campaign 1 that the highertemperature effected the leaching of a greater part of the sulfur in theconcentrate than the lower temperature of campaign 2.

[0016] On the basis of the color of the precipitate of the reactors, itwas possible to deduce that in test campaign 2, hematite started toappear in the solid matter from the second reactor (R2) onwards, and inthe last reactor (R4) the iron was mostly in the form of hematite. Intest campaign 1, the iron was mostly in the form of goethite even in thelast reactor. Approximations were confirmed also by X-ray diffractionanalyses. TABLE 1 Test Test Quantity campaign 1 campaign 2 Concentratefeed into reactor R1 g/h 260 240 Cu content of concentrate % 23.10 24.2Fe content of concentrate % 30.4 30.9 S content of concentrate % 37.034.5 Solution feed into reactor R4 L/h 2.11 1.49 Cu content of solutionfeed g/L 39.2 41.1 Fe content of solution feed g/L 0.41 0.0 Na contentof solution feed g/L 105 107 SO₄ content of solution feed g/L 4.5 0.0Air feed into reactor R1 L/min 0.0 1.9 Air feed into reactor R2 L/min8.9 5.0 Air feed into reactor R3 L/min 0.9 1.7 Air feed into reactor R4L/min 0.7 1.2 Total air feed L/min 10.5 9.9 Temperature in reactor R1 °C. 95 85 Temperature in reactor R2 ° C. 95 85 Temperature in reactor R3° C. 95 85 Temperature in reactor R4 ° C. 95 85 Average temperature ° C.95 85 Solid matter content in R1 g/L 116 363 Solid matter content in R2g/L 106 251 Solid matter content in R3 g/L 71 219 Solid matter contentin R4 g/L 41 105 Average solid matter content g/L 84 235 Cu content ofsolid matter in R4 % 0.87 1.08 Fe content of solid matter in R4 % 43.145.1 S content of solid matter in R4 % 13.5 21.6 Cu(kok) in solutionproduced g/L 66.3 78.1 in R1 Cu (²⁺) in produced solution g/L 14.6 19.7in R1 Fe in produced solution in R1 g/L 2.04 0.32 SO₄ in producedsolution in R1 g/L 18.3 10.5 Cu recovered in solution % 97.3 96.9

1. A method for the leaching of sulfidic, iron-bearing copperconcentrate in a chloride milieu in order to achieve an essentiallyiron-free, alkali chloride-copper chloride solution, and the recover ofiron and elemental sulfur as solid matter precipitate, where theconcentrate leaching is carried out continuously on the countercurrentprinciple and in several stages with the aid of bivalent copper andoxygen-bearing gas, characterized in that the copper concentrate isleached in atmospheric conditions at a temperature which at highestcorresponds to the boiling point of the solution, and that a longerdelay is arranged for the solid matter than the solution flow-through byreturning part of said solid matter to leaching contrary to the mainflow of the solid matter, wherein the iron is precipitated from theconcentrate mainly as hematite.
 2. A method according to claim 1,characterized in that the solid matter is returned, with regard to thedirection of solid matter flow, to any previous stage reactors, so thatthe leaching time of the solid matter is prolonged by at least twicecompared with leaching time without recycling.
 3. A method according toclaim 2, characterized in that at the end of every stage there isliquid-solid matter separation, of which the solid matter precipitateobtained as underflow is recycled to a reactor of any previous stage. 4.A method according to claim 2, characterized in that at the end of everystage there is liquid-solid matter separation, of which the solid matterprecipitate obtained as underflow is recycled to the first reactor ofany previous stage.
 5. A method according to claim 1, characterized inthat the solid matter is returned within the same stage, with regard tothe direction of solid matter flow, to the previous reactors, so thatthe leaching time of the solid matter is prolonged by at least twice,compared with leaching time without recycling.
 6. A method according toclaim 5, characterized in that at the end of every stage there isliquid-solid matter separation, of which the solid matter precipitateobtained as underflow is recycled to any reactor of the same stage.
 7. Amethod according to claim 5, characterized in that at the end of everystage there is liquid-solid matter separation, of which the solid matterprecipitate obtained as underflow is recycled to the first reactor ofthe same stage.
 8. A method according to claim 1, characterized in thatthe solid matter is recycled in the single reactor.
 9. A methodaccording to claim 1, characterized in that the amount of solid matterin the first reactor of the stage is at least 250 g/L.
 10. A methodaccording to claim 1, characterized in that leaching time of the solidmatter is at least 10 h.